The lengthened propellant tanks were thus also necessary in lieu of using more powerful fuel. The Mercury-Redstone designers rejected hydyne and returned to the standard ethyl alcohol fuel. Furthermore, hydyne had never been used with the new A-7 engine. This was a more powerful fuel than ethyl alcohol, but it was also more toxic, which could be hazardous for an astronaut in a launch pad emergency. The standard Redstone was fueled with a 75 % ethyl alcohol and 25 % LOX solution, essentially the same propellants as the V-2, but the Jupiter-C first stage had used hydyne fuel, a blend of 60 % unsymmetrical dimethylhydrazine (UDMH) and 40 % diethylenetriamine (DETA). Many of the more advanced Jupiter-C components were also removed for reliability reasons or because they were not necessary for Project Mercury. As a starting point, the most obvious step was getting rid of its staging capability as the Mercury-Redstone would not utilize upper stages. Hans Paul and William Davidson, propulsion engineers at the Army Ballistic Missile Agency (ABMA), were assigned the task of modifying the A-7 to be safe and reliable for crewed flights.ĭuring 1959, most of ABMA were preoccupied with the Saturn project, but those engineers who could find enough free time in their schedule were invited to work on man-rating the Jupiter-C. The Jupiter-C's engine, however, was being phased out by the Army, so to avoid potential complications such as parts shortages or design revisions, the Mercury-Redstone designers chose the Rocketdyne A-7 engine used on the latest military Redstone. Therefore, this Jupiter-C first stage was used as the starting point for the Mercury-Redstone design. The standard military Redstone lacked sufficient thrust to lift a Mercury capsule into the ballistic suborbital trajectory needed for the project however, the first stage of the Jupiter-C, which was a modified Redstone with lengthened tanks, could carry enough propellant to reach the desired trajectory. Army's Redstone liquid-fueled ballistic missile for its sub-orbital flights as it was the oldest one in the US fleet, having been active since 1953 and had many successful test flights. Comparison of Mercury-Redstone (right) with Redstone missile and Jupiter-C
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